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#26 alanh

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Posted 11 September 2005 - 12:20 AM

apsilon,
You have not said where you are. Click on Geographical Viewers' Forums. Subforums Select your geographic subforum and then open Get the best reception. Which transmitter and which antenna
Post any further posts on this topic in your geographic viewers’ forum.

The some masthead amplifiers come with filters included. Anything which is not wide band .

7seven
Kingray MHU44G B1-3 -1 dB, B4-5 44 dB

AlanH

#27 DoktorDigital

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Posted 09 May 2006 - 08:23 PM

thanks for your help bellotv appreciate it !!! is there anywhere where i can get more info on understanding the formulas for ber some of the readings are a bit strange to me like "1x10-4" etc



Carlton,

In order to understand BER, please use the following example:

BER = Bit Error RATIO (NOT RATE!) Rate is Incorrect terminology and means something totally different.
It is the ratio of errors present within the incoming data stream.
And is measured before and after viterbi / error correction.

Then... Usually a BER meter/instrument would normally display the 1x10-4 as a 1E-5
In any case, 1E-4 would mean
1 Error in every 10,000 Bits of Information (data) received.
Notice the (-4), you can make this the NUMBER OF ZEROS you must add to the initial number.

If your instrument is displaying a 10 before the Bit number, then it would equate to 10 + 0000 zeros. Ie: 100,000 but you will need to check on this from your user manual but logically I would bet it to be like this.

The same goes for 5E-3.
This would equate to: 5 errors in every 1,000 Bits received.
or 3E-2 would equate to 3 errors in every 100 bits received.
Of course, the less number of zeros (or you could call it the order of magnitude) the worst your signal is.
A bad signal would be 1E-2 and probably your signal is on the border line of falling off the cliff edge.
A fantastic signal would be 1E-8 (ie: a perfect incoming signal)
However, be aware...if you are getting 1E-8 AFTER viterbi (error correction) and a lower reading like 1E-3, then you would have to look at your antenna setup to try and get a better signal.
You really should aim for the best possible incoming signal measured BEFORE viterbi (error correction).

I hope this is easy enough for you to understand. If you still have trouble, please let me know and I will explain in a different way. But I am pretty sure you will understand now.

#28 DoktorDigital

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Posted 09 May 2006 - 09:02 PM

apsilon,
You have not said where you are. Click on Geographical Viewers' Forums. Subforums Select your geographic subforum and then open Get the best reception. Which transmitter and which antenna
Post any further posts on this topic in your geographic viewers’ forum.

The some masthead amplifiers come with filters included. Anything which is not wide band .

7seven
Kingray MHU44G B1-3 -1 dB, B4-5 44 dB

AlanH



AlanH,

Is there a reason why you always refer to Kingray?
They are not the best solution for the above problem!

There are many other Mast Head Amplifiers that will do the job better and WITH RF shielding for a much lower price and higher quality.
The MHU44G is NOT RF SHIELDED. IT IS IN AN ENTIRELY PLASTIC CASE! And very inviting for Impulse noise.

Maybe you can try a Fracarro JS2RT or even the Fracarro MAP series.

It all depends on the incoming signal.
If it is too strong and you use a high gain mast head, you will over drive the amplifier and destroy/clip the signal.

In your case you mentioned an MHU44G which has 44dB gain on UHF right?
However, if the incoming signal is very high like...say...70dBuV and because the MHU44G has a final output of 108dBuV, you will actually overload the amplifier because:

70+44=114dBuV (this is 6dB over the MAXIMUM Input allowed)
So sure, now you can say you will just turn down the input attenuator and sure that is fine.
You will need to attenuate by 6dB to get to the maximum allowed, but will you have minimum noise?
And remember that the MHU44G is an INPUT stage Amplifier, Not Mid stage so there is NO gain control! Just input attenuator so your noise factor is increased.

But what if the person in question has a huge signal like 85dBuV off the antenna straight to the TV outlet?
Many people make the mistake of thinking that because the set top box doesn't work or the analogue picture is bad, it must be because of low signal... Then by adding a masthead you actually make the problem even worse.

7seven, can you supply a CHANNEL POWER & CARRIER TO NOISE READING?
This would help greatly in solving your problem.

Sure you can also say that the signal received by the person in question might be very low, then that is a different story to a certain extent. But remember that the Kingray Masthead that you have recommended is NOT shielded but in a plastic case. For digital, this is NOT recommended!

Then, if you are using the mast head as a filter...well then there is something wrong with your thinking.
Filtering is done by filters, not mast heads unless you want to perform a multitude of operations at once which includes amplification.

Also, AlanH, I am not sure why you are saying that Salt spray will make digital reception pixelate and the sound to chirp. Among the many reasons why this could be happening, most of the time it is because of two things. Either too little or too much channel power or impulse noise but I am betting it would be impulse noise more than anything.

Digital TV is present in MANY countries INCLUDING countries that have a coast line like Australia, Italy or Vietnam for example. In both cases, salt spray is NOT a factor. It is usually Impulse noise or other reception factors.
But salt spray...that would have to be the most silly thing I have ever heard... sorry :blink:

#29 alanh

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Posted 09 May 2006 - 10:13 PM

Digital Docktor,
The reason I have been recommending Kingray is because of the internal filtering. I am looking a band pass filter of 174-230 MHz for band 3, 526 - 589 for band 4, 526 - 680 for band 4+ and 680 - 820 MHz for band 5.
In particular I do not want gain in the 45-174 MHz band.

This minimises interference and allows the maximum gain to be set. The only source of overload is other analog TV transmissions in that band. If yoiu can find others, then I will certainly recommend them.

As for shielding, the amount of metalwork in antennas particularly band 1 - 3 is considerably more than the input wiring to the first transistor of the masthead amplifier, so I would rather have a filter than shielding if I had to chose. So the antenna is a much better antenna than the wiring in the masthead amplifier.

I agree that overloads are a possibility These amplifiers contain gain controls. I also agree that an antenna which is restricted to the frequency range of interest and has adequate gain is preferable. Getting sufficient signal level from the amplifier through long cables is also important to minimise interference and overcoming cable loss. You will notice I have said this is general advice in the Geographic Viewers' forums. Here I have only recommended them for diffuse and weak signal areas.

The fact that masthead amplifiers can make the situation worse has come up many times on this forum.

Filtering can be anywhere but it must be prior to any amplifer and as close as possible to the input. Otherwise you get intermodulation . This will then "transfer" the interfering signal to the frequency of the channel being amplified. Then no filter can remove the interference. Putting the filter in a separate shielded box then makes is much more expensive because of the extra weather proof case, pcb, dicast box and connectors.

Salt, Australia is an island surrounded by ocean where most of the population live. The Mediterranean is a sea so is smaller.

The problem with salt is that it accelerates the corrosion of the steel screws (which connect to the down lead) and the aluminium they screw into. The oxides in rust are a semiconductor and as a result will cause the intermodulation mentioned above. I have seen analog pictures from a corroded antenna with the windscreen wiper effect. So for digital the inpulse interference will worsen as the corrosion increases.

The other problem with salt is that it gets on high voltage power line insulators. This causes them to arc when there is moisture. Typically at tea time! The arc will produce many frequencies gradually reducing in power as the frequency rises. However the power line is the aerial! Where I live the power company washes the salt from the insulators to prevent blackouts.

One poster lives near a 225 kV power line and can tell you all about it, even the acoustic noise you can hear from the power line.

AlanH

#30 M'bozo

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Posted 09 May 2006 - 10:45 PM

And remember that the MHU44G is an INPUT stage Amplifier, Not Mid stage so there is NO gain control! Just input attenuator so your noise factor is increased.



Oh give me a break please!

MHU44G pdf

I must be using a different product, there seems to be a midstage gain control in this model :blink:

Edited by marcj, 09 May 2006 - 10:55 PM.


#31 DoktorDigital

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Posted 09 May 2006 - 11:38 PM

Oh give me a break please!

MHU44G pdf

I must be using a different product, there seems to be a midstage gain control in this model :blink:


Marcj,

Yes I have clearly made a mistake in my comment. I did not see this pdf before I made that comment so I will give you that, but it doesn't change the gist of what was said.
It is funny you have pinpointed this particular thing though... No problem...
I will now be extremely alert and include some quotations of particular persons in the future :P

#32 DoktorDigital

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Posted 10 May 2006 - 01:22 AM

AlanH,

Sure you have selected the Kingray because of the band pass filtering...However, this doesn't change the fact that if you might have too much signal and you will over drive the amplifier and make the situation worse.

The first thing that should always be done before anything else would be to KNOW the ACTUAL signal received. I have never seen anyone ask a question on what type of Channel Power, CNR or BER this particular person is receiving at the outlet point.
Ie: the Channel Power and CNR of each individual carrier in the particular bands.
ONLY THEN can one make an informed decision of which type of mast head amplifier to use. And no one can argue with that. Without proper measurements, we are all flying blind.

Then...about shielding on mastheads and that you stated "As for shielding, the amount of metalwork in antennas particularly band 1 - 3 is considerably more than the input wiring to the first transistor of the masthead amplifier, so I would rather have a filter than shielding if I had to chose. So the antenna is a much better antenna than the wiring in the masthead amplifier." Sorry mate, that is absolutely rediculous!
Do you not know that many impulse noise problems ingress at the mast head and connection point and many times because of non existent shielding or even impedence missmatching... Even the masthead you recommended, it is a saddle and screw type. Not even F-Connector and also just plastic cover with NO SHIELDING. http://www.gme.net.a.../mhu_series.php

Also your comment QUOTE:"[color=#C0C0C0]Filtering can be anywhere but it must be prior to any amplifer and as close as possible to the input. Otherwise you get intermodulation . This will then "transfer" the interfering signal to the frequency of the channel being amplified. Then no filter can remove the interference. Putting the filter in a separate shielded box then makes is much more expensive because of the extra weather proof case, pcb, dicast box and connectors
."
[color=#000000]Well actually I agree with you, the filtering must be before the amplifier, but usually always at the headend. Imagine you have ingress at the headend but you insert a filter before a trunk amplifier down the network. That is just wasting time. However sometimes the interference is BEHIND the actual carrier that you are trying to reticulate and therefore not possible to filter with normal filtering. But this is very important because when it comes to Impulse noise or other similar type of interference, the problem occurs BEHIND the actual carrier that you are trying to reticulate and by using equipment that has NO shielding, you are making the probability much higher. And when you are mentioning about metal boxes etc... if you compare the fracarro product pricing to Kingray pricing, and remember that the Fracarro product is Shielded, the fracarro pricing is much lower in cost than Kingray and you get a better product anyway. And no I do not work for Fracarro.

Finally, about the salt issue. I'll have you know that I have lived on an island and other countries on the coast not far from Australia for many years and some of these places have digital and very salty atmosphere with high and low humidity. I can tell you that what you are saying is rediculous and extreme. Yes, the salt causes corrosion etc... but the actual problem here is IMPULSE noise. But sure, you can say that arcing is what is generating the impulse noise and I will give you that, but to say it in this context is quite silly. There could be 10s of different reasons why there is impulse noise present.
In the islands and other countries that I have lived in, and have both sat and terrestrial digital, problems were generally because of impedence missmatching, ingress, poor connections/connectors, poor quality cable, non earthing of headend or antennas, mercury vapour lighting and dirty motors... the list goes on and on. Not once has there been an incident which was caused by overhead high voltage electrical cables arcing when there is moisture unless of some extreme scenario.

Even the poster that lives near a 225kv power line can talk about the Audible acoustic noise that they can hear, doesn't mean that this is the reason for the pixelisation. In the end, BER, Channel Power and CNR (all together) are extremely important. If all parameters are comfortably correct and you have pixelisation problems, then you can start looking at impulse noise etc... but I would be starting with the house lighting, any motor driven equipment even nearby, or even checking the actual TV system if that is the case... Has this person checked every single RF connector? Are all connections F-Type? What type of antenna?, what type of mast head (if any)? what type of cable used?, what type of outlet wall plate used?, what type of fly lead? Is there an impedence missmatch in the system? etc... The electrical power lines would be the last thing that would be looked at. Could even be that the signal received is just hanging off the edge of the cliff. But without actually Measuring the channel power, CNR & BER, no one can say what the cause is, not even myself. Sorry :blink:

#33 M'bozo

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Posted 10 May 2006 - 08:07 AM

Yes I have clearly made a mistake in my comment. I did not see this pdf before I made that comment so I will give you that, but it doesn't change the gist of what was said.
It is funny you have pinpointed this particular thing though... No problem...
I will now be extremely alert and include some quotations of particular persons in the future :blink:



OK.

I am simple. As I have used this particular item the error was obvious.

There was also a sense of deja-vu, but I can't quite put my finger on it........ think I'll go on another holiday.

Marc.

#34 M'bozo

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Posted 10 May 2006 - 05:25 PM

I know the sense of dejavu now.

New poster appears plugging Fracarro. (along with making sensible observations)

?Is he Poidahl/Peter/Pietro in another guise?

So would the good Herr Doktor Digital care to explain for me what his agenda is here? I wouldn't want to be misguided. :blink:

Marc.

#35 DoktorDigital

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Posted 10 May 2006 - 06:54 PM

Marcj,

No guise here. Just want to give my 2 cents just like everyone else but I am tired of reading stuff that is just not true.

And no I am not any of the above persons you mentioned either. :blink:
And I do not know who poidahl is (i can't even pronouce the name), but I know who peter and pietro are and I can assure you I am not any of them in disguise.

However, Yes I have obviously dealt with them on a business level because I purchase my stock from laceys, OBVIOUSLY, but I can assure you I am not one of those persons. I did, however, go to uni with one of those persons but I will not say who :P
Bloody Typical...of course because I am plugging Fracarro you would be so suspicious to think that I am working for the aforementioned persons and I have an alterior motive...sorry to dampen your hopes :P

What about AlanH, is he working for GME Kingray maybe? He seems to plug kingray all the time???
Maybe he is taking a bit of payola on the side for plugging kingray on this site for so long!
Why are you not suspicious of him like you are with me? Absolutely Rediculous...

#36 cofdmstuff

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Posted 10 May 2006 - 07:26 PM

Marcj,

No guise here. Just want to give my 2 cents just like everyone else but I am tired of reading stuff that is just not true.

And no I am not any of the above persons you mentioned either. :blink:
And I do not know who poidahl is (i can't even pronouce the name), but I know who peter and pietro are and I can assure you I am not any of them in disguise.

However, Yes I have obviously dealt with them on a business level because I purchase my stock from laceys, OBVIOUSLY, but I can assure you I am not one of those persons. I did, however, go to uni with one of those persons but I will not say who :P
Bloody Typical...of course because I am plugging Fracarro you would be so suspicious to think that I am working for the aforementioned persons and I have an alterior motive...sorry to dampen your hopes :P

What about AlanH, is he working for GME Kingray maybe? He seems to plug kingray all the time???
Maybe he is taking a bit of payola on the side for plugging kingray on this site for so long!
Why are you not suspicious of him like you are with me? Absolutely Rediculous...


Hi there Dok

I suppose you were once an excellent installer who has managed to climb up the ladder now right?

Everyone here is allowed to give his 2c worth of info...without an attitude and AlanH doesn't have one.

Cheers

PS: I suppose you use Unaohm as well right?

#37 DoktorDigital

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Posted 10 May 2006 - 07:46 PM

Hi there Dok

I suppose you were once an excellent installer who has managed to climb up the ladder now right?

Everyone here is allowed to give his 2c worth of info...without an attitude and AlanH doesn't have one.

Cheers

PS: I suppose you use Unaohm as well right?


Hi there cofdmstuff

No actually I am still an installer!
And I do not have an attitude either. Maybe I'm a little raw and people can sometimes take that the wrong way because I say what I think but... thats life I guess :blink:
Maybe I might have to take diplomacy classes :P

P.S. Actually I have two instruments. One is a Rhoden Swartz and the other is a Kathrein.
And I have a HP network analyzer too.

Cheers

#38 alanh

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Posted 10 May 2006 - 07:56 PM

Digital Docktor,

Firstly, I have no business connection at all with any manufacturer, wholesaler or retailer despite what you may have been told.

On overload I have mentioned this possibility in my Geographic Viewers' Posts where masthead amplifiers are only mentioned in weak signal areas. As for antenna basics this area is already covered. Measuring the signal levels to prevent overload is always a good idea. However there is nothing to stop a strong signal from local arcing from modulating a weak TV signal within the amplifier even to the point of clipping. Hence filtering.

I do not understand this technical term behind. There is nothing stopping you putting another filter in prior to distribution if there is a long cable from the antenna to the distribution point. The point is that filters should be prior to amplification to prevent intermodulation.

I have not been concerned about pricing provided the best result is achieved. That is a customer's choice.

Causes for BER to be poor.
Poor signal to carrier ratio. If the signal level through the antenna system is low and local impulse interference is high the BER will be high. If however the signal level in the antenna system is high then the local impulse noise will be a smaller proportion of the signal and will havel less effect on the BER

Momentary gaps in signal and poor shielding will let the impulse interference in due to poor cabling and connectors. The other factors I agree with.

You do not live in an area where the electricity company has many pole top fires caused by the arcing I mentioned every autumn. At one stage they lost power to a major city for more than a week! Just because you have not experienced it does not mean it does not happen. I would not expect Melbourne to have much of a problem with this because it is not on the ocean.

You should remember that the first radio transmissions were from spark gap transmitters which is what all arcing sources are. They have a wide bandwidth right up into the VHF band. The way they affect the BER is that the arcing signal is going to change the data being received. Error correction can only work so far. The measurement of BER would have to be instantaneous and not average values to pick these effects up.

Impulse interference is so bad this is why the ACMA made the decision not to allocate any digital transmissions below 174 MHz. (channel 6)

I would like to reiterate that I have recommended Fracarro products on my lists and would be happy to recommend any amplifiers which have filtered inputs to the channel combinations we use.

Finally you mentioned in another post that the Fracarro Log Periodic antennas have the CAI seal of approval. This is straight from the Fracarro Website. Unfortunately the CAI is an British organisation. The UK does not use band 3 for free to air TV. The European scene is so croweded with stations that band 4-5 antennas are mostly used. In Australia we have band 3 predominating, and the ACMA has selected band 3 & 4 only for capitial cities, band 4+ for high powered regional areas (where possible) and band 5 for low powered repeaters. We can optimise the antennas required. We also have a huge country where as in Europe congestion is a big thing and long distance is not considered.

We also use mobile communications, UHF CB and pagers in the European channels 21-28 which can also cause poor BER due to interference.

We also use vertical polarisation extensively which changes antenna requirements.

So do not blindly quote other countries' experiences that should apply in Australia.

AlanH

#39 James T Kirk

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Posted 10 May 2006 - 08:17 PM

AlanH and DoktorDigital

What's going on here gents. Lots of advice, diagreement and yet where there's agreement you are both wrong

Firstly I smell a rat here somewhere, I cannot conceive of someone have a piece of Rohde and Schwarz equipment and making such an abysmal effort in spelling the name.

One glaring error is that the fact is on amplification is that you don't always have to have the filter before first amplifier. You two have pressed the opposing view so often either you simply have no idea what you are talking about or limit your experience to what you can get from a Dick Smith or Jaycar catalogue.

Wake up you two, if you don't know what you are talking about, keep it to yourselves.
The poor sods whose only reference is this web site just need the facts.

James

#40 DoktorDigital

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Posted 10 May 2006 - 08:52 PM

Alanh,

Hmmm...

On overload I have mentioned this possibility in my Geographic Viewers' Posts where masthead amplifiers are only mentioned in weak signal areas. As for antenna basics this area is already covered. Measuring the signal levels to prevent overload is always a good idea. However there is nothing to stop a strong signal from local arcing from modulating a weak TV signal within the amplifier even to the point of clipping. Hence filtering.


Actually masthead amplifiers are also used in Metro areas where the signal is extremely low such as valley like areas in the CBD (sydney melbourne brisbane). However, it should be mentioned that you should ALWAYS measure the signal at each and every job. If an installer is using a portable tv to check the signal, then they are not a professional installer and should go and do something else because it just gives our specialized profession a bad name.

The technical term BEHIND could be explained by:
Imagine you have a spike or another digital carrier, which could be referenced as interference (ie: 2MHz wide/bandwidth) and at a channel power of 50dBuV with CNR of 30dB referrenced to 235MHz. The actual placement or frequency of this "interference" is at 225MHz on the terrestrial band.
Now combine this "Interference" into a signal that is received from your antenna and lets use channel 12 Digital for this example..
Now tell me how to filter this "interference" with a normal filter???
I bet you can't - and no, you do not know where the interference carrier is coming from but let's just say it is some uni student playing around with some rf gear but you cannot tell him to turn it off.
Also because this is an example, you can not answer this by saying that you will call the ACMA and ask them to terminate this interference. This example is only to help you understand the point I am trying to get across to you.

I have not been concerned about pricing provided the best result is achieved. That is a customer's choice.


actually you said in the earlier post...

Putting the filter in a separate shielded box then makes is much more expensive

so I don't understand what you are saying here???

Then...

Causes for BER to be poor.
Poor signal to carrier ratio. If the signal level through the antenna system is low and local impulse interference is high the BER will be high. If however the signal level in the antenna system is high then the local impulse noise will be a smaller proportion of the signal and will havel less effect on the BER


Actually, what causes poor BER are many things but I think you are trying to say is LOW CARRIER to NOISE, NOT Signal to Carrier (maybe you made a typo here???). But Impulse Noise and Earth/system Noise (related to physics) are two different things here. Maybe you are tired today...
But...the fact of the matter is that the smaller the Carrier To Noise Ratio (that is the smaller the Carrier in Relation to the Noise), the worst BER you will have. Remember that the CARRIER is the messenger of data to the receiver. If there is not enough data (ie: large enough carrier in relation to the noise factor) then the receiver cannot display an image.
Impulse noise is different but will have the same effect as the "Interference" as stated above.

You do not live in an area where the electricity company has many pole top fires caused by the arcing I mentioned every autumn. At one stage they lost power to a major city for more than a week! Just because you have not experienced it does not mean it does not happen. I would not expect Melbourne to have much of a problem with this because it is not on the ocean.


How do you know where I live and where I have lived in the past. In one of my earlier posts I mentioned that I lived on some islands and other countries along the coast. So why do you say that I have not experienced anything ???

And

Impulse interference is so bad this is why the ACMA made the decision not to allocate any digital transmissions below 174 MHz. (channel 6)


well, this is a subject that posess great passion for in this country. In actual fact, just by putting 7MHz carriers in the VHF band just made life all the more difficult for everyone.
NEARLY the whole world runs on 8MHz channels (and no i did not say everyone) and where digital is concerned, MOST countries have allocated them in UHF @ 8MHz.
I don't know what it is but we always have to do things the hard way here in Australia...for what reason??? God only knows...

And as far as what other countries do, I have lived in many countries (I am 45 years old) and I can tell you that there are other countries that use Band 3 for FTA TV. If you like I can provide you with links to different sites if you want to be convinced or even better, google search the stuff and you can try and prove me wrong. Good luck... However yes, the CAI have approved the LP45N Log periodic, but that doesn't mean that the LP345 will not perform in a similar manner. I believe you understand what I am saying but maybe you don't like it because I am not talking about hills or something???
Finally, I will have you know that many countries use Vertical Polarization, including Italy, so don't be so quick to quote on other countries if you do not know anything about them.

Doktor Digital

#41 DoktorDigital

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Posted 10 May 2006 - 09:03 PM

James T Kirk,

Mate, I never said I am perfect and I am the first to admit it...
And sure, I made a typo (Rhode & Schwarz) sure I forgot the "ch" and ??? what is your point here?

Can you give a constructive REASON why you think that if it is an error that you don't ALWAYS have to put the filtering behind the first amplifier?
Give us all an example of your reason and intelligence why this is the case!

Go on, please enlighten all of us... I am eagerly awaiting your interesting and enlightening reply !
(of course you must follow the same context of what was said)

P.S. And there is no rat here. Just a very interesting debate. No hard feelings, just trying to get to the facts...

Cheers :blink:

#42 James T Kirk

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Posted 10 May 2006 - 09:38 PM

DoktorDigital

Smelling a rat:

I looked at the quality of your written word, very few spelling mistakes and those that are there can be attributed to typo's. Then there's "Rhoden Swartz", spelt it as if you have never seen it written before, it just doesn't gel.

It is a point of particular frustration when I am challenged to explain something that if you had any real grasp of the subject you would know when to back off. However for the purposes of assisting those others reading here the reason is as follows.

The advice to place a filter before the amplifier is general and good advice that will give significant improvement in the huge majority of cases. It is also the safest option for installers with little experience.

There are however situations where the amplifier should be used first.
Classically these are situations where there is very marginal wanted signal levels and yet C/N (carrier to noise ratio) is reasonable and at the same time some local significant signals are present. In this situation if the filter is placed before the amplifier, the filter's insertion loss eats into the already marginal signal.
By originally placing a very linear low gain (10-20dB) amplifier stage prior to the filter and careful positioning of the receive antenna, these losses are overcome and the resulting signal will present the receiver with a better C/N ratio without the intermods the uninitiated might expect. This is no theory, it's in use and delivers superior results in this application.

James

#43 alanh

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Posted 10 May 2006 - 09:46 PM

Docktor Digital,
I have not disagreed with you about measuring signal levels, and have recommended it in posts.

As for behind see the post on about Penrith. The interfering signal can easily be removed by a filter provided it is before any non linear circuit. Ie an amplifier. Afterwards its too late.

As for separate filters, it is much easier to add the small coils and surface mount capacitors with the amplifier on the same circuit board, than house them separately and it will perform better.

You are right about carrier to noise ratio. As far as this is concerned we are saying the same thing. If the carrier to noise ratio is low the BER will be high, however if the C/N ratio is large and the BER is high it is likely to be delayed signals & interference and reflections in the cabling.

As far as RF band width is concerned all transmissions in the Americas are 6 MHz wide, in Europe VHF is 7 MHz wide and at UHF it is 8 MHz. This then requires all receivers to have 2 SAW IF filters for dual bandwidth.

Here we have the same number of channels available as in Europe but we have 56 MHz for mobile communications.

If you look at the Geographic Viewers' Forums you will find viewers receiving signals over large distances 80 km is not uncommon.

The salt story is true.

AlanH

#44 DoktorDigital

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Posted 10 May 2006 - 11:48 PM

James, you are just trying to wind me up. What alterior motive could I possibly have behind a spelling mistake? You are taking this totally out of context and you sound like one of those ignorant so and so's who say that they've been in the industry for 40 years, and they know everything...

Yet when I ask you a very simple question to give an explanation on why the filter before the amplifier is not important, you answer it with such a rediculous example. You obviously have no idea of how RF works and you should go back to school and learn before you open your mouth or write about such silly things.

You say that you analysed all my previous posts and how the majority of the spelling is correct, yet you have failed to understand what was written and the context of the discussion.
If you had read properly, you would have understood what we were talking about and that is completely different to what you have mentioned here. And still, you have no idea what you are talking about. But I like a challenge, so I will back my comments up with fact! Not like you do

Here is why...
If you have two carriers (but each carrier is a DIFFERENT service ie: Channel A & Channel B ) on the same frequency, there is no way you can take out the un-wanted channel with the type of filtering you described.
The only way you can eliminate the unwanted channel is by positioning the antenna so that it receives the least amount of the unwanted carrier. As to what you are saying, its absolutely crap! There is no way you can filter out that channel (IF ON THE SAME FREQUENCY AS DESCRIBED ABOVE) by inserting a filter after an amplifier stage of any gain. By Amplifying the particular Channel (ie: the full 7-8MHz bandwidth where BOTH carriers are present) all you are doing is just that...AMPLIFYING BOTH CARRIERS !

Still don't believe me...ok, just set up two analogue modulators (reason for analogue is because Digital modulators are out of most people's budget) and set BOTH modulators for channel 50 (681.25MHz).
Now connect the RF output of One of the modulators to a 2 way splitter (in reverse) and connect the output (which was the input) of the 2 way splitter to your spectrum analyser and view the actual TV picture (which the modulator is obviously connected via A/V to a video source different to the second modulator).
Now without taking your eyes of the picture, connect the RF output of the SECOND modulator to the Second port of the 2 way splitter (in reverse) and turn the modulator on and see what happens to the picture now.
This is with analogue! and you can imagine what happens to the data in digital. (This of course is just an example but I believe gets the message across).
Now try and use that silly filtering example that you made before to fix the picture...I bet you cannot!
Now who looks silly?

Also, CNR, In Digital scenario, is not the most important factor. You can have a fantastic CNR and channel power but if you have an interference behind the wanted carrier, your BER will suffer.
Also CNR measurements are referenced to another frequency which has NO carrier, but just noise present.
And if you have carrier A that has a CNR of 40dB and carrier B (which is behind carrier A so to speak) which has a CNR of 25dB (if you could measure it that is - or turn off the transmitter that is transmitting carrier A), then your true CNR would be 15dB by rights.
And although BER and CNR are mathematically related, doesn't mean that if you have a good CNR you will necessarily have a good BER.

You just don't know what you are talking about and suggest you go back to school to learn RF and English and stop trying to baffle people with bulldust. Your example makes absolutely no sense whatsoever!
So if you want to continue to make a fool of yourself, keep tit for tatting... But I CHALLENGE YOU TO PROVE WHAT YOU SAY IS CORRECT! Good luck :blink: Otherwise give it a rest! :P

#45 DoktorDigital

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Posted 11 May 2006 - 12:24 AM

AlanH...this could go on forever... :P

Just a quick one before I stop posting on this subject...

I agree with you about filtering MUST be BEFORE the amplifier so we are saying the same thing but in a different way. It's just good ol james.t.kirk that can't get his brain around the concept. Not sure he ever will :blink:

Same goes for Carrier to noise, we are saying the same thing.
And yes, in the USA is 6MHz just like Japan, all the way through all bands (of course NTSC). And Europe is 7MHz VHF and the Superband (PAL). But 8MHz in the Hyper/external Superband and UHF so no gripe with you there either.
And yes I agree that viewers are receiving channels from 80km away is also possible. I never said it wasn't. Even further with the right antenna and optimal atmospheric conditions...the ionosphere can do marvelous things with RF in the right conditions!

But, although your salt spray example could be real, it is not the reason why everyone that is near high voltage powerlines experience pixelation.

Anyway...

#46 James T Kirk

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Posted 11 May 2006 - 07:07 AM

DoktorDigital

Not even close my friend. Try another forum to wind people up. Knowing you cannot filter out in band interference with a filter is pretty basic. Try reading what was written and with experience over time you may learn how to describe it technically.

James

#47 DoktorDigital

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Posted 11 May 2006 - 09:18 AM

James,

hehehehehehehehe...Very poor comeback...try telling us how to ACTUALLY filter it out rather than a meaningless reply like that... :blink:
It just shows that you are full of BS and nothing constructive to say!

Go on, I challenge you to tell all of us how to filter the second carrier WITHOUT removing the number 2 input and putting a filter AFTER the splitter or imaginary amplifier...Try to PROVE me wrong instead of just saying I don't know...I want to know how to do it because you are such a knowledgeable person...
GO ON we are all waiting :P :P :P

#48 James T Kirk

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Posted 11 May 2006 - 01:26 PM

DoktorDigital

I didn't come down in the last shower sonny, stop trolling and wearing out your keyboard with very long explanations of what the technically savvy can pass on in a few lines.

By the way, who were you last week before you decided to try DoktorDigital?

On the other hand, if you are genuinely unable to grasp what I have already described fully in very simple terms, then I apologise because there is little I can do for you!

James

#49 bellotv

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Posted 11 May 2006 - 07:47 PM

Doktor digital
I,m only a mere TV technician /antenna installer and not an RF engineer like yourself or James but I interprete from what James is trying to say is that as a typical filter has an insertion loose of around 1-2dB,If you put it after the amp you would get a better carrier to noise at the outputthan if you put it before the amp.
I also interprete that he is suggesting that this is only suitable where unwanted singals will not be so high as to overload the amplifier and he recommends using amplifiers that a very linear so that intermodulation is minimized.
He is not saying that it will remove the "behind signal".Infact he mentions careful positioning of antenna to address this issue.

There is logic in this method especially if you are in a very terminally weak area to squeeze out the last drop from the antenna.

Otherwise you have said some intersting things.

I liked and finally understood your last description of the "behind signal" ,Der finally get your point.

This sounds like the argument of why MER is more important than CNR because it is a measure of the channel and the behind the channel interferrer.

#50 DoktorDigital

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Posted 11 May 2006 - 11:34 PM

James...get a life...you have got no idea what you are talking about and now everything is getting out of hand. There is no need to offend me by calling me a troll.

But you are yourself so ignorant of RF that you have not understood one word that was written in my posts.
They are long because if I don't bloody cover every single possible angle, there will always be a smartass like you to pick on a hole that I have left out. This is typical of people that know nothing and profess that they know everything...Like YOU James!

And if you continue to reply on this thread, you will see that you are only showing everyone how silly you are for the simple FACT OF THE MATTER THAT YOU CANNOT EVER ANSWER ANY OF MY QUESTIONS OR CHALLENGES WITH ANY REAL TECHNICAL FACTS... ALL YOU DO IS INSULT!

You either give some constructive arguments so we can debate this like civilized persons or just shut the hell up! Simple like that!